Simulating quantum 'time travel' disproves butterfly effect in quantum realm:
Using a quantum computer to simulate time travel, researchers have demonstrated that, in the quantum realm, there is no "butterfly effect." In the research, information—qubits, or quantum bits—'time travel' into the simulated past. One of them is then strongly damaged, like stepping on a butterfly, metaphorically speaking. Surprisingly, when all qubits return to the 'present,' they appear largely unaltered, as if reality is self-healing.
[...] In the team's experiment, Alice, a favorite stand-in agent used for quantum thought experiments, prepares one of her qubits in the present time and runs it backwards through the quantum computer. In the deep past, an intruder—Bob, another favorite stand-in—meaures[sic] Alice's qubit. This action disturbs the qubit and destroys all its quantum correlations with the rest of the world. Next, the system is run forward to the present time.
According to Ray Bradbury, Bob's small damage to the state and all those correlations in the past should be quickly magnified during the complex forward-in-time evolution. Hence, Alice should be unable to recover her information at the end.
But that's not what happened. Yan and Sinitsyn found that most of the presently local information was hidden in the deep past in the form of essentially quantum correlations that could not be damaged by minor tampering. They showed that the information returns to Alice's qubit without much damage despite Bob's interference. Counterintuitively, for deeper travels to the past and for bigger "worlds," Alice's final information returns to her even less damaged.
"We found that the notion of chaos in classical physics and in quantum mechanics must be understood differently," Sinitsyn said.
The more damage you do in the past, the less the present is affected?
(Score: 4, Insightful) by BsAtHome on Thursday July 30 2020, @07:57AM (9 children)
The result then begs the question whether or not the universe is deterministic.
Is the outcome predetermined if changes made to the initial state do not propagate? That would also mean that the world of quantum probabilities may collapse into a (or the same) deterministic system regardless the initial state. Funny then, that we can't determine anything at the quantum level when its result at the macro level apparently does not change.
(Score: 3, Informative) by leon_the_cat on Thursday July 30 2020, @08:37AM
https://www.technologyreview.com/2019/03/12/136684/a-quantum-experiment-suggests-theres-no-such-thing-as-objective-reality/ [technologyreview.com]
(Score: 5, Informative) by aristarchus on Thursday July 30 2020, @08:51AM (5 children)
NO!!!!! It does not "beg the question"! In that case, it would just be arguing in a circle! Like, "the universe is deterministic because everything in it is necessary consequence of a cause". That is question begging. Or, "things happen for no reason, because there is no reason for things to happen". THAT is begging the question. Now just RAISING the question (my ancient Greek Hecate god, how many times do we have to go over this!) of whether the universe if deterministic or totally random and nonsensical to the point where no rational being could even
begraise the question of whether it was, . . . well, we have answered that, then, haven't we? Unless those rational beings cannot even grasp the meaning of "begs the question". Then we are all truly fucked.I like to cite Grammar Girl, since she gets it wrong: https://www.quickanddirtytips.com/education/grammar/begs-the-question [quickanddirtytips.com]
And, of course, the Grammarist: https://grammarist.com/rhetoric/begging-the-question-fallacy/ [grammarist.com]
Of course, for the handy business cards: http://begthequestion.info/ [begthequestion.info]
Now write it one hundred times! Ex Romani Domus Petitio Principii Excoriatorum.
(Score: 5, Funny) by leon_the_cat on Thursday July 30 2020, @09:03AM (1 child)
lol u need some catnip.
(Score: 0) by Anonymous Coward on Thursday July 30 2020, @07:04PM
What he really needs is a mirror
(Score: 0) by Anonymous Coward on Friday July 31 2020, @07:02AM (1 child)
It's an idiomatic phrase. The individual words in the phrase don't matter, just the use of the phrase as a whole, and "begs the question" to mean "raises the question" is far more common to the point where people bringing up the issue of something assuming the conclusion is true will just outright say the words "assumes the conclusion".
In fact, the fucking name in that latter sense is still idiomatic, because it's a terrible, terrible translation of the Latin phrase (which was also altered a bit from the Greek it derived from).
(Score: 2) by aristarchus on Friday July 31 2020, @10:16AM
You are begging the question. Or looking for a beating. It is a technical usage, and the common usage is based on an illiterate similarity. The Greek is nothing like the Latin, it is τὸ ἐξ ἀρχῆς. So your entire objection is something of a damp squid. It is rough to be stupid and wrong like this, but at least it is better than being stupid and right, because it gives you plausible deniability.
(Score: 2) by corey on Friday July 31 2020, @11:15AM
Bloody hell, he got a +5 and I don't have any idea what he said!
(Score: 4, Interesting) by Non Sequor on Thursday July 30 2020, @02:13PM (1 child)
Any system is deterministic if you mutliplex the hell out of it so that all possible initial conditions are paired off with possible outcomes in a many to many relationship. Nondeterminism comes from picking a specific thread.
This is a consequence of the linearity of quantum mechanics. It's easiest to follow for the discrete time model using matrix mechanics. (You can approximate the continuous time, general system case from discrete time systems of qubits.) You have a system state (as a linear combination of pure states) at time zero and you have a evolution operator U that represents performing some interaction (e.g. applying a magnetic field) on the system for a time increment. U acts on pure states (e.g. electron with known spin) in the same linear way as it acts on mixed states (e.g. electron with known superposition of up and down states or experimental ensemble of random up and down states). Each state gets mapped to one or more outcomes, proportional to the probability amplitude for that state (think of it as the fraction of the system that is in that state). Linear.
Your operator U is unitary, meaning that it preserves the fact that the probability amplitudes for all of the pure states that make up the superposition sum to 1. Being unitary means that U is invertible and that in fact its inverse is its conjugate transpose. If you have solved for a matrix that represents a forward time increment for a system, it is trivial to calculate the matrix for undoing the interaction you've performed. If you are simulating that matrix in a quantum computer, you can just as easily simulate the reverse direction with the same number of qubits. This is a peculiarity of quantum mechanics: there is nothing particularly special about the way processes run forward in time. On paper, time reversal is generally equally plausible. With quantum field theory, time reversal does impose the condition that all charges need to be flipped and the position coordinates need to be mirrored for both directions to obey the laws of physics, but these are not really radical distinctions between forward time and reverse time.
So move time one direction, disturb the system, move time the other direction, the influence of the disturbance is linear. This is at odds with the classical result where most non-trivial systems exhibit exponential sensitivity to disturbances in initial conditions (chaos). This kind of feels like a variation on Lochsmidt's paradox: you can't derive the second law of thermodynamics from time-symmetric dynamics. On the other hand, gravity, which has resisted description as a quantum phenomenon has a distinct time-asymmetry: the charges for gravity are all positive and the time reversal does not obey the same law of gravity as the forward time version. There's not a complete picture of how to reconcile all of this.
Write your congressman. Tell him he sucks.
(Score: 2) by corey on Friday July 31 2020, @11:17AM
Yeah this is another one, +4 and I got two sentences in. Maybe people are modding because it sounds informative?
(Score: 3, Informative) by EJ on Thursday July 30 2020, @09:08AM (3 children)
No, Phoenix666. The farther in the past you DO the damage the less the present is affected.
(Score: 4, Touché) by kazzie on Thursday July 30 2020, @09:12AM (2 children)
So killing my own grandfather is risky, but killing my great-great-grandfather is safe?
(Score: 4, Informative) by c0lo on Thursday July 30 2020, @09:38AM (1 child)
Only if your great-great-grandfather had a quantum nature. Ummm.. was he ever locked in a box observed by Schrödinger?
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by DeVilla on Friday July 31 2020, @01:38AM
Maybe he was ... maybe he wasn't.
(Score: 4, Insightful) by anubi on Thursday July 30 2020, @09:31AM (1 child)
I use device models all the time with computer analysis. Using models, I can build devices with phenomenal performance.
However I usually can't build a physical device that has that kind of performance. My model is simply a model. Not exact. I learned long time ago that one should always verify that something really works by building one and verifying it does what it's supposed to do.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 2) by sjames on Friday July 31 2020, @01:36PM
This. Models and simulations are all implemented based on theory. They cannot show anything that theory doesn't predict.
They can be useful in cases where we don't fully understand the implications of a theory, and they can be compared to a physical experiment to see how well our theory does against reality.
Notably, what they did here was not actually sending the qbit back in time. If it was, the story would be
Alice gets ready to create a qbit and exclaims "OH! I seem to have already done it, that's odd"
(Score: 1, Interesting) by Anonymous Coward on Thursday July 30 2020, @09:44AM
No time to do it properly though.
I do find the abstract/introduction broken though:
the way I read it, they say they get a system to evolve according to nonlinear equations, then perturb it, then evolve backwards. and then they find that the perturbation doesn't affect the outcome that much (system still ends up in more or less the same state).
either I'm reading it wrong, or what they did isn't really a big deal unless they prove that the backwards equations also have positive Lyapunove exponents for the component that they perturb.
in simple english: if I let ping-pong ball roll of the top of an upturned bowl, I can't predict which direction it will go. If I move it around while it's on the floor, and then reverse the dynamics (I push it uphill), then I can guarantee that it will get to the top of the bowl no matter how much I messed with it while it was on the floor.
this scenario has not been ruled out by these people as far as I can tell.
(Score: 3, Interesting) by ledow on Thursday July 30 2020, @12:55PM (2 children)
I'm gonna go into my personal way of understanding quantum effects here, don't take this as scientifically rigorous.
Most quantum effects can be explained by the particles involved not actually being restricted to our classical four dimensions.
These things are traversing entire other dimensions, co-exist in them, and are able to move around in them without the limitations of distance in our dimension, and thus provide "spooky actions at a distance". The same way you move left, or right, they can move "out" or "in" our universe on other dimensions. They're still bound by rules, but rules that we haven't formulated to take account of them. They can zip through our universe and appear to come from nowhere and disappear, but that's just our visualisation of their actions, to them, they are just moving "left" which takes them through our universe and back out.
To entangled particles, they aren't millions of miles apart, they were quantumly-entangled and in the other dimensions used they are still linked (somehow, it's very hand-wavy) and thus even though they are miles apart here, the extra dimensions are shortcut and they are essentially still "touching" each other. They're bound by the rules of our dimensionality but have one foot in another dimension which lets them shortcut, cheat and do things we would think impossible in classical physics.
And time is just another dimension to them. They may not even be strictly limited to our uni-directional time, they may be able to pop in and out of time, or be linked to objects through time just the same as with their spatial dimensions, or even go backwards in time, or not be affected by time at all any more than you are affected by "left" (i.e. you can move left and move opposite-to-left, but you aren't bound by the rules of "left"). It's very difficult to pin down.
When you start thinking that way, a lot of quantum effects can be explained. Some particles can "borrow" energy that they don't have, from nowhere, and use it, so long as they pay it back later on. To them, it may well be that the energy was in their "past" (our future" or some perpendicular timeline), so they didn't break any rules of their own, they just look like they are breaking our rules.
But, generally, with all those extra dimensions to play in, they are still bound by a larger set of laws of physics, which means that they still "repay" the energy, or they still "get damaged" or whatever... just not in what dimensions we can see, and in what timeline direction we witness.
I believe the maths (and quantum physics is basically someone solving quite-normal equations, realising the answers blow out of all proportions and provide weird and "impossible" answers, and then over a hundred years we've realised the answers are perfectly correct, but that the way they apply to us requires us to think in far more than the classical four dimensions) basically says we need 11-or-more dimensions to adequately resolve the equations in question, and that means that quantum physics - the stuff we found when we went LOOKING for the results of these impossible answers - likely also operates in 7-or-more dimensions that are impossible for us to directly perceive. One of those could be another time dimension, who knows? Or we may be odd creatures that only perceive time in one direction whereas particles and the universe see it as bidirectional (it does seem rather odd that the maths for 3D extends to 4D and there's little or no explanation for how/why/if that fourth-dimension should be one-way at all... it's mathematically just the same as the others in many respects).
When you start thinking like that, results like this become weird curiosities rather than inconcievable nonsense. We damage the particle. But the particle is not operating entirely within our dimensions or time. What's to say that the "effect" of that damage won't take effect until a billion years from now when it next crosses a particular point in another dimension?
Quantum stuff is weird. And so is relativity, which has essentially the same types of mathematical problems. We work from perfectly normal, ordinary maths. All of a sudden, an awkward question proposes an incredibly complicated and high-dimension answer (a bit like dividing by all the numbers, and then you hit zero... or taking square roots perfectly happily and then you go beyond zero into negative numbers... same maths, but the way you normally handle it goes boom!), and the only explanation that fits is that there are far more dimensions than we can perceive.
And yet, when those impossible answers happen, by chance, to come back to "ordinary numbers" later in the calculations, they *exactly match reality*. So particle pop back into existence in our universe, or the maths works out to make the classical energy equations correct, or whatever. If it was just a quirk where the answer was "just don't do that", then that wouldn't happen, but it does. Which suggests that our mathematical "to the power 11" is far more than just some numbers on paper, but reflective of the reality of the universe, and moving from powers of 2 to powers of 3 to powers of 4, etc. which all match and determine reality doesn't fundamentally change just because we're including dimensions that we have no direct perception of.
As a mathematician, I love the idea that the maths is unchanged and unbroken and perfect, and it's merely our concept of reality that's forced to conform to it in order to make any sense, not the other way around.
(Score: 2, Disagree) by Common Joe on Thursday July 30 2020, @01:31PM (1 child)
It sounds like you're arguing for parallel worlds -- which I would say isn't strict time travel.
(Score: 2) by ledow on Thursday July 30 2020, @02:43PM
It's the same, in both. It's not parallel worlds as such - that would be further dimensions like ours that are out there running other universes like ours.
Just extra dimensions to our own. It's like earth people suddenly realising they could go "up" rather than just along the lay of the land.
It's not (necessarily) lots of universes next door, it's the same universe but with dimensions that we don't use, where particles (but not necessarily even substantial matter) have always had all the dimensions, we just never used/witnessed them.
We're 3.5D beings in an 11+D universe. There's nothing to suggest that our D's are anything special at all, and it would be odd if our D's were "replicated" somehow... it's the same set of D's most likely.
But (0,0,0,0) in our universe is really (0,0,0,0,0,0,0,0,0,0,0), and those last digits changing just means that we're not part of the world. It's like being on a perfectly straight railroad track and then realising you could build another at right-angles to it. Somewhere in there, when you travel along the new track, there may be other railroads heading in the same direction as our original, but, of course, being dimensionally separate, we'd never have known about them.
And with time being just the fourth 0, we have no idea where it would be possible to travel along that. But it would be time travel. It might show us our past railroad, or our future railroad, or we might cross paths with other railroads. It's no different to any other dimension - when we near "0" on that co-ordinate, we near our origin point/time. When we stray from it, we get further away in distance/time in one direction or another.
But there's nothing to say that when you're at (0, 0, 0, 0, 10000000, ....) that there's any way to tell our universe at (0,0,0,0) even exists. You're so far away, you'd never know.
To a particle that can just traverse any set of coordinates because the maths lets it, and it ends up with a velocity on one of those extra dimensions, we'd appear to distance ourselves until it returned to something near our coordinates. And it would disappear from our existence entirely because we can only see the first four, and only a tiny fraction of one of those (i.e. what's here NOW).
When dimensions are just coordinates, and travelling is just maths on a certain axis, then time travel is just heading in a certain direction, no different to walking off to the side of the railroad.
(Score: 0) by Anonymous Coward on Friday July 31 2020, @05:08AM
another phys.org turd